ADDKESS. Ixxvii 



we luivo an iListrumout by lucaus of which the heigM of the tido at .1 given 

 port can be accuratclj' predicted for all times of the day and night. 



The attraction-meter of Siemens is an instrument of great delicacy for 

 measuring horizontal attractions, which it is proposed to use for recording 

 the attractive influences of the sun and moon, upon -which the tides depend. 

 The bathometer of the same able physicist is another remarkable instrument, 

 in which the constant force of a spring is opposed to the variable pressure of 

 a column of mercury. By an easy observation of the bathometer on ship- 

 board, the depth of the sea may be approximately ascertained without the 

 use of a sounding-line. 



The Loan Exhibition of Apparatus at Kensington has been a eomploto 

 success, and cannot fail to be useful, both in extending a knowledge of 

 scientific subjects and in promoting scientific research throughout the country. 

 Unique in character, but most interesting and instructive, this exhibition 

 will, it is to be hoped, be tlie precursor of a permanent museum of scientific 

 objects, which, like the present exhibition, shall be a record of old, as well 

 as a representation of new inventions. 



It is often difficult to draw a distinct line of separation between the phy- 

 sical and chemical sciences ; and it is perhaps doubtful whether the division 

 is not really an artificial one. The chemist cannot, indeed, make any large 

 advance without having to deal with physical principles; and it is to Eoyle, 

 Balton, Gay-Lussac, and (Jraham that we owe the discovery of the mecha- 

 nical laws which govern the properties of gases and vapours. Some of these 

 laws liave of late been made the subject of searching inqiiiry, which has 

 fullj- confirmed their accuracy, when the body under examination approaches 

 to what has not inaptly been designated the ideal gaseous state. But when 

 gases are examined under varied conditions of pressure and tcmperatiu-e, it 

 is found that these laws are only particular cases of more general laws, and 

 that the laws of the gaseous state, as it exists in natiire, although they may 

 be enunciated in a precise and definite form, are very diflferent from the 

 simple expressions which apply to the ideal condition. The new laws be- 

 come in their turn inapplicable when from the gaseous state proper wo 

 pass to those intei-mediate conditions which, it has been shown, link with 

 unbroken continuity the gaseous and liquid states. As wc approach the 

 liquid state, or even when we reach it, the problem becomes more com- 

 plicated ; but its solution even in these cases will, it may confidently be 

 expected, yield to the powerful means of investigation we now possess. 



Among the more important researches made of late in physical chemistrv, 

 I may mention those of F. Weber on the specific heat of carbon and the 

 allied elements, of Berthelot on thcrmo-chemistry, of Eunsen on spectrum 

 analysis, of Wiillner on the band- and line-spectra of the gases, and of 

 CUithrie on the cryohydrates. 



C'osmicnl chemistrv is a science of vesterdav : and vet it alreadv nbonjuls in 



